Bath: You can make beneficial biochar at home

Sep. 6, 2013

One of the most fascinating developments in horticulture is the rediscovery of biochar, a charcoal manufactured for horticulture.

Biochar used as a soil amendment is believed by the majority of researchers to hold unparalleled promise in advancing and improving both conventional and biological growing, while a minority argues the potential is exaggerated.

In my experience, biochar is everything it portends to be, an ancient knowledge now analyzed through the lens the scientific method, enabling us to understand just how it functions and allowing us to improve the material. Of all the customers that have relayed anecdotal feedback, I’d say more than 90 percent report exceptional results, often at application rates far less than the textbooks suggest.

Biochar is a charcoal made through a specific process that accentuates the horticultural properties for use as a soil amendment. Customers often wonder if they can use charcoal purchased for grilling, or charcoal found in the burn areas following forest fires. The answer really is ... potentially. My understanding based upon research and experience shows that you should really know how the charcoal was made, as variables such as cooking temperature, direct or indirect pyrolysis, ash content, feedstock and other factors will ultimately determine the quality of charcoal to be used.

Currently, I recommend either you make your own or purchase horticultural grade biochar.

The properties that make biochar desirable for altering soil dynamics rest mostly with porosity and surface area. Properly made biochar will exhibit between 4,000 and 12,000 square feet of surface area due largely to the microporosity of the char. The porosity and surface are provided for the sorptive capacities, allowing biochar to absorb and store nutrients, air and water while also providing structure for the colonization by beneficial bacteria and mycorrhizae (fungus).

Biochar acts like apartment complexes for the inhabitant microbes that remain the quintessence of organic and biological growing. Many of the profound benefits resulting from biochar are related to the powerful synergistic effect it has with microbes. In addition, smaller particles of biochar introduce oxygen into the soil and isolate clay particles, insulating their electric charge and making the soil less sticky and compact and more suitable for growing.

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Biochar can be made at home by the more adept and assiduous practitioner. Instructional videos and manuals are found on the internet, but working with fire and high temperatures can be dangerous, so do so cautiously. Biochar is made through a process known as pyrolysis; the charcoal is heated either directly with flame, or indirectly in a segregated container. I have found the indirect production method produces a much higher quality product, as the volatiles are not entirely burned off resulting in an oily sheen, compounds that have been shown to benefit soil biology.

Controlling the temperature also is critical; firing should be kept between 500 and 1,000 F as higher temperatures will reduce surface area and porosity. Although some research has found that these qualities can be restored with CO2 or steam treatment, it is much simpler to manage the firing temperature.

For both these reasons wildfire remnant charcoal is not ideal, although it could be useful, and I would recommend avoiding grilling charcoal, as the method of manufacture and purity cannot be verified. Next week I will discuss several steps necessary to properly prepare biochar for use in the garden.

Spencer Bath of Fort Collins can be found at Bath Garden Center and Agri-charge.com.